Mixtures of organo-tin compounds

ABSTRACT

Mixture consisting of an organo-tin alcoholate of the formula (I) ##STR1## and of an organo-tin mercaptide of the formula (II) or (III) ##STR2## which mixture additionally contains an organo-tin carboxylate of the formula (IV) or (V) ##STR3## in which formulae R 1  is C 1  -C 12  alkyl, R 2  is C 10  -C 30  alkyl, phenyl which is substituted by one or two C 8  -C 12  alkyl groups, R 3  has the meaning assigned to R 2  or is the --Sn(OR 2 )(R 1 ) 2  group, wherein R 1  and R 2  are as defined above, X is sulfur or oxygen, R 4  is the --S--CH 2  CH 2  --COOR 5  or --X--Sn(R 1 ) n  (S--CH 2  CH 2  --COOR 5 ) 3-n  group, in which R 1  and X are as defined above, R 5  is C 8  -C 14  alkyl, n is 1 or 2, and R 6  is C 10  -C 30  alkyl, the weight ratio of I:II or I:III being in the range from 9:1 to 1:9. These mixtures are stabilizers for chlorinated polymers and also activators for the manufacture of foamed plastics.

This application is a continuation, of application Ser. No. 396,526, filed July 8, 1982 abandoned.

The present invention relates to mixtures of organo-tin compounds and to chlorinated polymers and foamed plastics materials which contain these mixtures.

Mixtures consisting of an organo-tin mercaptide and an organo-tin compound selected from the group consisting of organo-tin, organo-tin carboxylate, organo-tin alcoholate or organo-tin oxide, are described as effective thermostabilisers in German Offenlegungsshcrift No. 1 926 949. A mixture consisting of an organo-tin thioglycollic acid ester and an organo-tin compound as described above is specifically disclosed in this publication.

As it is known that organo-tin mercaptides lower the impact strength of rigid polymers, there is considerable interest in highly effective stabilisers which can be employed in small amounts.

Organo-tin compounds are also employed as activators for the manufacture of foamed articles composed of plastics. These articles are ordinarily manufactured by known methods, for example by injection moulding, by blending the plastics material with a suitable blowing agent and choosing the processing temperature such that it is above the decomposition temperature of the blowing agent. Often, however, the decomposition temperature is too high above the processing temperature, so that the blowing agent cannot be used alone. For this reason, activators are often employed which hasten the decomposition of the blowing agent and/or lower the decomposition temperature.

German Offenlegungsschrift No. 2 444 991 describes an activator system consisting of organo-tin oxides, organo-tin alcoholates, or of mixtures thereof.

It has now been found that a mixture of organo-tin compounds and of an organo-tin mercaptopropionic acid ester imparts surprisingly good light and heat stability to chlorinated polymers and, in addition, is an effective activator for the manufacture of foamed plastics.

Accordingly, the present invention provides mixtures consisting of an organo-tin alcoholate of the formula (I) ##STR4## and an organo-tin mercaptide of the formula II or III ##STR5## which mixtures may additionally contain an organo-tin carboxylate of the formula (IV) or (V) ##STR6## in which formulae R¹ is C₁ -C₁₂ alkyl, R² is C₁₀ -C₃₀ alkyl, phenyl which is substituted by one or two C₈ -C₁₂ alkyl groups, R³ has the meaning assigned to R² or is the --Sn(OR²)(R¹)₂ group, wherein R¹ and R² are as defined above, X is sulfur or oxygen, R⁴ is the --S--CH₂ CH₂ --COOR⁵ or --X--Sn(R¹)_(n) (S--CH₂ CH₂ --COOR⁵)_(3-n) group, in which R¹ and X are as defined above, R⁵ is C₈ -C₁₄ alkyl, n is 1 or 2, and R⁶ is C₁₀ -C₃₀ alkyl, the weight ratio of I:II or I:III being in the range from 9:1 to 1:9.

The invention also provides mixtures consisting of an organo-tin mercaptide of the formula II or III ##STR7## and an organo-tin carboxylate of the formula IV or V ##STR8## in which formulae the symbols have the meanings assigned to them in claim 1, the weight ratio of II:IV or III:IV being in the range from 9:1 to 1:9.

R¹ as C₁ -C₁₂ alkyl is e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-amyl, iso-amyl, n-hexyl, n-heptyl, n-octyl, n-dodecyl. Preferably, R¹ is methyl, n-butyl, n-amyl, n-hexyl and n-octyl. Most preferably, R¹ is methyl, n-butyl and n-octyl.

R² and R³ as C₁₀ -C₃₀ alkyl can be decyl, dodecyl, isotridecyl, tetradecyl, hexadecyl, 16-methylheptadecyl, nonadecyl, 2-eicosyl, docosyl, cetracosyl or hexacosyl. Preferably, alkyl groups R² and R³ contain 10 to 22 carbon atoms. Preferred alkyl groups R² and R³ are iso-tridecyl and tetradecyl. R² and R³ as phenyl which is substituted by one or two C₈ -C₁₂ alkyl groups can be e.g. p-octylphenyl, p-(2-ethylhexyl)-phenyl, p-nonylphenyl, p-(3,7-dimethyloctyl)-phenyl, 3,5-dinonylphenyl. p-Nonylphenyl is especially preferred.

Where R³ is the group --Sn(OR²)(R¹)₂, R¹ and R² are the same radicals as described above.

R⁴ can be group --S--(CH₂ CH₂ --COOR⁵, wherein R⁵ is C₆ -C₁₄ alkyl, e.g. 2-ethylhexyl, decyl, dodecyl, isotridecyl, tetradecyl. R⁵ is preferably 2-ethylhexyl, dodecyl and isotridecyl, especially 2-ethylhexyl and isotridecyl.

R⁴ can be the group --X--Sn(R¹)_(n) (S--CH₂ CH₂ --COOR⁵)_(3-n), wherein X, R¹, R⁵ and n are as defined above. Preferably, R⁴ is --S--CH₂ CH₂ --COOR⁵.

R⁶ as C₁₀ -C₃₀ alkyl is e.g. decyl, dodecyl, isotridecyl, tetradecyl, iso-octadecyl, nonadecyl, docosyl, hexacosyl.

Preferably, R⁶ is C₁₀ -C₂₂ alkyl, most preferably 16-methylheptadecyl, iso-nonyl and n-undecyl.

Examples of compounds of the formula I are: dibutyl-tin ditetradecyl oxide dibutyl-tin di-isotridecyl oxide dibutyl-tin-bis-(p-octylphenyl oxide) dioctyl-tin bis-(p-nonylphenyl oxide) dioctyl-tin (ditetradecyl oxide) bis(dibutyl-p-nonylphenyloxy-tin)oxide bis(dioctyl-p-octylphenyloxy-tin)oxide bis(dibutyl-isotridecyloxy-tin)oxide bis(dibutyl-tetradecyloxy-tin)oxide.

Preferred compounds of the formula I are dibutyl-tin ditetradecyl oxide, dibutyl-tin diisotridecyl oxide, and dibutyl-tin bis-(p-nonylphenyl)oxide.

Examples of compounds of the formula II are: octyl-tin tris(dodecyl-β-mercaptopropionate) dibutyl-tin bis(isotridecyl-β-mercaptopropionate) dibutyl-tin bis(2-ethylhexyl-β-mercaptopropionate) bis(dibutyl-tin 2-ethylhexyl-β-mercaptopropionate)oxide.

The preferred compound of the formula II is dibutyl-tin bis(2-ethylhexyl-β-mercaptopropionate).

A preferred example of the compound of the formula III is butyl(2-dodecyloxycarbonylethylmercapto)-tin sulfide.

Examples of the compounds of the formula IV are: dibutyl-tin dilaurate bis(dibutyl isodecanoyl-tin)oxide dibutyl-tin di-isooctadecylate.

The preferred compound of the formula IV is dibutyl-tin di-isooctydecylate.

The chlorinated polymers which contain the stabiliser mixture of the invention can be homopolymers, e.g. polyvinyl chloride, polyvinylidene chloride etc. Suitable polymers are emulsion, suspension and mass polyvinyl chloride. The polymers can also be copolymers which have been obtained by copolymerising vinyl chloride or vinylidene chloride with other ethylenically unsaturated monomers. Ethylenically unsaturated monomers are compounds which contain polymerisable. C-C double bonds, and comprise acrylates, e.g. acrylic acid, ethyl acrylate, acrylonitrile; vinyl monomers, e.g. styrene, vinyl acetate; maleic acid derivatives, e.g. maleic acid, maleates, maleic anhydride.

The mixtures of this invention can also be employed as activators for foaming plastics materials. These plastics materials can be chlorinated polymers, such as those described above; but polyesters, polylactones, polyamides, polyethers, polycarbonates and, preferably, polyols, are also suitable.

It is especially preferred to use the mixtures of this invention in polymers based on polyvinyl chloride, especially in PVC, viz. both in plasticised PVC and in rigid PVC. Rigid PVC which has been stabilised with the mixtures of this invention is most suitable for external use.

Organo-tin alcoholates as activators are known from German Offenlegungsschrift No. 2 444 991. Organo-tin alcoholates and organo-tin carboxylates as light and heat stabilisers for halogenated polymers have been described in the above mentioned German Offenlegungsschrift No. 1 926 949 in combination with organo-tin mercaptocarboxylates. These latter are also known from U.S. Pat. No. 3,642,677.

The organo-tin oxides can be obtained in known manner by hydrolysis of the corresponding organo-tin halides. Organo-tin alcoholates can also be obtained in known manner from the corresponding organo-tin halides with sodium alcoholate or from organo-tin oxides with alcohol. The organo-tin carboxylates can be obtained by simple reaction of the alkali salts of the acid in question with a water-soluble salt of tin.

A particularly uncomplicated method of manufacture is to react the alcohol, carboxylic acid, mercaptan and tin reactants simultaneously.

The amount of organo-tin compounds in the substrates depends on economic and technical aspects. As a rule, 0.1 to 3% by weight, based on the polymer, especially 0.3 to 2% by weight, is added. The weight ratio of organo-tin compounds of the formulae I:II, I:III, II:IV or III:IV in the mixtures of the invention is 9:1 to 1:9, preferably 9:1 to 6:4.

If desired, it is possible to add to the stabilised polymer mixtures of the invention 0.1 to 5% by weight, preferably 0.5 to 3% by weight, of conventional additives, especially antioxidants, light stabilisers or mixtures thereof. Examples of such additives are:

antioxidants, such as 2,6-dialkylphenols, e.g. 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2-tert-butyl-4,6-dimethylphenol, the β-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid ester of pentaerythritol (IRGANOX 1010) or the same ester of stearyl alcohol (IRGANOX 1076), and others such as bisphenol A, UV-absorbers and light stabilisers such as 2-(2'-hydroxyphenyl)benztriazoles, 2,4-bis(2'-hydroxyphenyl)-6-s-triazines, 2-hydroxybenzophenones, 1,3-bis-(2'-hydroxybenzoyl)benzenes, esters of unsubstituted or substituted benzoic acids, acrylates, and also nickel compounds, sterically hindered amines, oxalic diaaides, or other additives, e.g. plasticisers, lubricants, emulsifiers, fillers, carbon black, asbestos, kaolin, talc, glass fibres, pigments, fluorescent whitening agents, flame retardants, antistatic agents.

The mixture of organo-tin compounds of this invention can be blended with the polymer by known methods in known mixing devices. To this end, it is possible to add the blowing agent for foamed plastics material together with the organo-tin activator, or to blend the activator with a plastics material which already contains the blowing agent. In order to obtain as homogeneous mixtures as possible, it is advantageous to blend the individual components in powder form. It is possible, however, to use plastics granulates, in which case a binder can additionally be employed for better adhesion of the blowing agent and/or the organo-tin activator.

The mixtures of the present invention are surprisingly effective heat and light stabilisers. Owing to their excellent light protective action, the stabilised polymer is especially suitable for external use. In addition, the mixtures of the invention are surprisingly effective activators for the manufacture of foamed plastics.

The invention is illustrated in more detail by the following Examples, in which parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 Dibutyl-tin dialcoholate

37.5 g (0.15 mole) of dibutyl-tin oxide are reacted with 61.0 g (0.30 mole) of a technical mixture of about 36% of lauryl alcohol and about 64% of myristyl alcohol (average molecular weight about 203) in boiling toluene, while removing the water of reaction. The toluene is then removed, affording a colourless fluid which, on standing, slowly solidifies to a wax-like substance.

The product obtained contains a mixture of 36% of lauryl alcohol and 64% of myristyl alcohol.

Sn (found): 18.0%, n₂₀ ^(D) =1.4715.

EXAMPLE 2 Dibutyl-tin bis(-2-ethylhexyl-β-mercaptopropionate)

25.0 g (0.1 mole) of dibutyl-tin oxide is reacted with 43.6 g of 2-ethylhexyl thiopropionate at 110° C. under a water jet vacuum until the water of reaction has been completely removed.

Sn (found): 17.1%; n₂₀ ^(D) =1.5015.

The stabiliser mixture results when the 30% of the compound obtained is mixed with 70% of dibutyl-tin dialcoholate (from Example 1) at about 70° C. (n₂₀ ^(D) =1.4786).

EXAMPLE 3 (Simultaneous reaction)

Mixture of

I. (C₄ H₉)₂ Sn(--O--i--C₁₃ H₂₇)₂,--(30.0%)

II. (C₄ H₉)₂ Sn(--S--CH₂ CH₂ --COO--i--C₁₃ H₂₇)₂ and--(29.6%)

IV. (C₄ H₉)₂ Sn(--OOC--i--C₁₇ H₃₅)₂ --(40.4%)

62.7 g of dibutyl-tin oxide (0.25 mole) are reacted in 350 ml of boiling toluene with 36.0 g (0.18 mole) of iso-tridecanol, 56.1 g (0.18 mole) of isostearic acid and 41.6 g (0.14 mole) of isotridecyl thiopropionate, while removing the water of reaction. The toluene is then removed, affording 195 g of a colourless fluid.

Sn (found): 14.15%; n₂₀ ^(D) =1.4831.

The weight ratio of I:II is 1:1.

EXAMPLE 4 (Simultaneous reaction)

Mixture of

I. (C₄ H₉)₂ Sn(--O--i--C₁₃ H₂₇)₂,--(20.4%)

II. (C₄ H₉)₂ Sn(--S--CH₂ CH₂ --COO--i--C₁₃ H₂₇)₂ and--(52.0%)

IV. (C₄ H₉)₂ Sn(--OOC--i--C₁₇ H₃₅)₂ --(27.6%)

32.15 g (0.129 mole) of dibutyl-tin oxide are reacted in 150 ml of boiling toluene with 12.91 g (0.065 mole) of iso-tridecanol, 20.08 g (0.065 mole) of iso-stearic acid and 37.18 g (0.129 mole) of isotridecyl thiopropionate, while removing the water of reaction. The toluene is then removed, affording a colourless fluid.

n₂₀ ^(D) =1.488.

The weight ratio of I:II is 1:2.5.

EXAMPLE 5

V. (C₄ H₉)Sn(OOC--C₁₁ H₂₃)--O--Sn(C₄ H₉)₂ (OOC--C₁₁ H₂₃)--(70%)

II. (C₄ H₉)₂ Sn(--S--CH₂ CH₂ --COO--i--C₈ H₁₇)₂ --(30%)

39.6 g (0.159 mole) of dibutyl-tin oxide are reacted with 31.8 g (0.159 mole) of lauric acid at 110° C. while removing the water of reaction. The resultant fluid reaction product is mixed with 30 g of dibutyl-tin bis(2-ethylhexyl-β-mercaptopropionate) obtained in accordance with Example 2.

Sn (found): 24.5%, n₂₀ ^(D) =1.4928.

The weight ratio of II:V is 1:2.3.

EXAMPLE 6 (Simultaneous reaction)

Mixture of

I. (C₄ H₉)₂ Sn(--O--i--C₁₃ H₂₇)₂ --(28.6%)

II. (C₄ H₉)₂ Sn(--S--CH₂ CH₂ --COO--i--C₁₃ H₂₇)₂ --(28.8%)

IV. (C₄ H₉)₂ Sn(--OOC--i--C₁₇ H₃₅)₂ --(38.6%) +IRGANOX 1076--(4%)

32.7 g (0.13 mole) of dibutyl-tin oxide are reacted in 150 ml of boiling toluene with 18.8 g (0.09 mole) of isotridecanol, 29.2 g (0.09 mole) of isostearic acid and 21.7 g (0.07 mole) of isotridecyl thiopropionate, while removing the water of reaction. After the toluene has been removed, 4.0 g of Irganox 1076 are dissolved in the residue. After filtration, a fluid having the following characteristic data is obtained.

Sn: 15.0%

d₂₀ : 1,021

n₂₀ ^(D) : 1,4817

The weight ratio of I:II is 1:1.

EXAMPLE 7

Mixture of

I. (C₄ H₉)₂ Sn(--O--i--C₁₃ H₂₇)₂ --(13.3%)

II. (C₄ H₉)₂ Sn(--S--CH₂ CH₂ --COO--i--C₁₃ H₂₇)₂ --(28.8%)

IV. (C₄ H₉)₂ Sn(--OOC--i--C₁₇ H₂₅)₂ --(4%) +IRGANOX 1076

COMPONENT 1 (dibutyl-tin alcoholate-carboxylate)

21.0 g (0.08 mole) of dibutyl-tin oxide are reacted in 150 ml of boiling toluene with 39.3 g (0.13 mole) of isostearic acid and 8.4 g (0.04 mole) of isotridecanol, while removing the water of reaction. The toluene is then removed by distillation.

COMPONENT 2 (dibutyl-tin isotridecyl-bis-thiopropionate)

8.9 g (0.036 mole) of dibutyl-tin oxide are reached at 110° C. with 20.46 g (0.072 mole) of isotridecyl thiopropionate, while removing the water of reaction by distillation.

67.2 g of component (1) and 28.8 g of component (2) are mixed at 50° C. and then 4.0 g of Irganox are dissolved in the mixture. After filtration, a liquid having the following characteristic data is obtained.

Sn: 14.2%

d(20°): 1.033

n₂₀ ^(D) : 1,4861

The mixture ratio of I:II is 1:2.1.

EXAMPLE 8

Mixture of

    ______________________________________                                         I.                                                                                   ##STR9##                 (16.0%)                                         II.  (C.sub.4 H.sub.9 ) .sub.2Sn(SCH.sub.2 CH.sub.2COOi-C.sub.8 H.sub.17).          sub.2                     (19.0%)                                         IV.  (C.sub.4 H.sub.9 ) .sub.2Sn(OOCi-C.sub.17 H.sub.35).sub.2                                                (61.0%)                                         +    IRGANOX 1076               (4.0%)                                         ______________________________________                                    

23.8 g (0.096 mole) of dibutyl-tin oxide are reacted at 110° C. with 10.5 g (0.049 mole) of nonylphenol and 44.4 g (0.143 mole) of isostearic acid, while removing the water of reaction. The resultant liquid reaction product is mixed with 19.0 g of dibutyl-tin bis(2-ethylhexyl-β-mercaptopropionate) and 4.0 g of Irganox 1076.

Sn (found): 14.6%; n₂₀ ^(D) =1.4862.

The weight ratio of I:II is 1:1.2.

APPLICATION TESTS EXAMPLE 9 Static heat test

(a) A dry blend consisting of 100 parts of PVC (Solvic 264 GA; Deutsche Solvay-Werke). 0.2 part of lubricant (Wax E, Hoechst AG), 0.2 part of Tinuvin 320 (2-[2'-hydroxy-3',5'-di-tert-butylphenyl]-benztriazole) and 2.5 part of the stabiliser mixture of Example 2, is rolled for 5 minutes at 180° C. on mixer rolls, and afterwards samples of sheet with a thickness of 0.3 mm are taken.

The samples are subjected to heat in an oven at 180° C. and every 15 minutes the thermal ageing of a sample is determined according to the Yellowness Index (Y.I.) of ASTM D 1925-70.

    ______________________________________                                         Yellowness Index (Y.I.)                                                        time in mins.                                                                            15     30     45    60   75   90   105                               ______________________________________                                         Y.I.      14.8   17.7   19.5  22.5 28.6 34.8 72.4                              ______________________________________                                    

(b) The test is carried out by the same method as described in (9a), except that the dry blend consists of the following constituents: 100 parts of PVC (Vestolit P 1973 K), 4 parts of TiO₂, 0.2 part of lubricant (Wax E, Hoechst AG), 2.5 parts of stabiliser mixture.

    ______________________________________                                         Yellowness Index (Y.I.)                                                        time in mins.                                                                            15     30     45   60    75   90   105                               ______________________________________                                         Y.I.      8.6    10.2   12.1 13.9  16.5 19.6 33.8                              ______________________________________                                    

EXAMPLE 10 Mill ageing test

A dry blend consisting of 100 parts of PVC (Vestolit HIS 6882), 4 parts of TiO₂ and 2.5 parts of stabiliser mixture of Example 5 is subjected to a mill ageing test at 200° C., and samples are taken at 3 minute intervals to determine the Yellowness Index.

    __________________________________________________________________________     Yellowness Index (Y.I.)                                                        time in                                                                        mins.                                                                              3 6 9 12 15 18 21 24 27 30 33 36                                           __________________________________________________________________________     Y.I.                                                                               6.7                                                                              7.4                                                                              8.3                                                                              9.0                                                                               9.9                                                                               11.5                                                                              12.5                                                                              14.3                                                                              16.9                                                                              20.7                                                                              28.2                                                                              37.7                                         __________________________________________________________________________

EXAMPLE 11 Weathering test

100 parts of PVC are mixed with 0.2 part of Tinuvin 320 and 2.5 parts of the stabiliser mixture of Example 2 in a highspeed mixer. The mixture is rolled to a sheet for 5 minutes at 180° C. on a laboratory roll mill, and from this sheet a 0.5 mm transparent sheet is pressed at 180° C. on a daylight-press. This sheet is exposed to an accelerated weathering test (Xenotest 150 lamp, Original Hanau Quarzlampen GmbH, Hanau, West Germany). The weathering cycle comprises 29 minutes exposure to xenon-arc radiation and 1 minute exposure to artificial rain. Exposure is effected in rotation. In the table below, h indicates the total weathering time in hours. The test values indicate the course of yellowing (Yellowness Indices).

    __________________________________________________________________________     Yellowness Index (Y.I.)                                                        Time                                                                              600.sup.h                                                                         1200.sup.h                                                                        1800.sup.h                                                                        2400.sup.h                                                                        3000.sup.h                                                                        3600.sup.h                                                                        4200.sup.h                                                                        4200.sup.h                                                                        4800.sup.h                                                                        5400.sup.h                                                                        6000.sup.h                                                                        6600.sup.h                                                                        7200.sup.h                                                                        7800.sup.h                                                                        8400.sup.h                        __________________________________________________________________________     Y.I.                                                                              3.5                                                                               3.6                                                                               3.6                                                                               5.4                                                                               5.2                                                                               4.7                                                                               4.8                                                                               4.8                                                                               6.8                                                                               8.4                                                                               10.1                                                                              11.4                                                                              10.0                                                                              12.8                                                                              23.7                              __________________________________________________________________________

EXAMPLE 12

The weathering test as described in Example 12 is repeated, except that 100 parts of PVC (Vestolit HIS 6882), 4 parts of TiO₂ and 2.5 parts of stabiliser mixture are used, and exposure is effected with a Xenotest 1200 lamp. The test results are reported in the following table.

    __________________________________________________________________________     Yellowness Index (Y.I.)                                                        Time  600.sup.h                                                                         1200.sup.h                                                                        1800.sup.h                                                                        2400.sup.h                                                                        3000.sup.h                                                                        3600.sup.h                                                                        4200.sup.h                                                                        4800.sup.h                                                                        5400.sup.h                                                                        6000.sup.h                                    __________________________________________________________________________     stabiliser of                                                                        7.3                                                                               5.0                                                                               5.1                                                                               4.7                                                                               3.8                                                                               4.0                                                                               4.1                                                                               3.9                                                                               4.2                                                                               3.8                                           Example 6                                                                      stabiliser of                                                                        4.8                                                                               4.2                                                                               4.1                                                                               4.3                                                                               3.7                                                                               3.8                                                                               3.6                                                                               3.5                                                                               4.1                                                                               3.9                                           Example 7                                                                      __________________________________________________________________________

EXAMPLE 13

The weathering test of Example 11 is repeated using a dry blend consisting of 100 parts of PVC (Vestolit HIS 6882), 4 parts of titanium dioxide and 2.5 parts of the stabiliser mixture of Example 5. The results are reported in the following table.

    ______________________________________                                         Time 0       2400.sup.h                                                                             4800.sup.h                                                                             7200.sup.h                                                                           9600.sup.h                                                                             12000.sup.h                         ______________________________________                                         Y.I. 8.2     5.2     4.8     4.1   4.4     5.7                                 ______________________________________                                    

Even after 1200^(h) weathering, the sheet exhibits no discolouration.

EXAMPLE 14 Activator effect

10 parts of dioctyl phthalate and 2 parts of azodicarboxamide are mixed with 1 part of the stabilizer mixture of Example 2 as activator, and this mixture is kept at a constant temperature of 180° C. in a flask. The flask is connected to a gas burette and the amount of gas evolved is read off at specific intervals of time. The following result is obtained.

min.: 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 10.0

ml: 29 33 36 46 62 104 143 156 169 189 228 

What is claimed is:
 1. In a foamed polyvinyl halide composition made by using a blowing agent, the improvement which comprises using as the activator for the blowing agent, from 0.1% to about 3% by weight of the polymer of a mixture comprising an organo-tin alcoholate of the formula (I) ##STR10## and an organo-tin mercaptopropionate of the formula (II) or (III) ##STR11## in which formulae R¹ is C₁ -C₁₂ alkyl, R² is C₁₀ -C₃₀ alkyl or phenyl which is substituted by one or two C₈ -C₁₂ alkyl groups, R³ has the meaning assigned to R² or is the --Sn(OR²)(R¹)₂ group, wherein R¹ and R² are as defined above, X is sulfur or oxygen, R⁴ is the --S--CH₂ CH₂ --COOR⁵ or --X--Sn(R¹)_(n) (S--CH₂ CH₂ --COOR⁵)_(3-n) group, in which R¹ and X are as defined above, R⁵ is C₈ -C₁₄ alkyl and n is 1 or 2, the weight ratio of I:II or I:III being in the range from 9:1 to 1:9.
 2. A composition according to claim 1, wherein R³ in the compound of the formula (I) has the same meaning as R².
 3. A composition according to claim 1, wherein R¹ in the compound of the formula (I) is C₁ -C₈ alkyl and R² and R³ are C₁₀ -C₂₂ alkyl.
 4. A composition according to claim 3, wherein R¹ is n-butyl. and R² and R³ are iso-tridecyl.
 5. A composition according to claim 1, wherein R² and R³ in the compound of the formula (X) are phenyl which is substituted by one or two C₈ -C₂₂ alkyl group.
 6. A composition according to claim 1, wherein R⁴ in the compound of the formula (II) is the --S--CH₂ CH₂ --COOR⁵ group, in which R⁵ is C₈ -C₁₄ alkyl.
 7. A composition according to claim 6, wherein R⁵ is 2-ethylhexyl. 